Time-resolved spectroscopic diagnostic of the CO2 plasma induced by a high-power CO2 pulsed laser

Laser-induced breakdown spectroscopy of CO2 plasma, initially at room temperature and pressures ranging from 6.4 to 101 kPa was investigated using a transverse excitation atmospheric CO2 pulsed laser (λ = 10.532 μm, a full width at half maximum of 64 ns, and an intensity from 1.2 to 5.6 GW cm−2). The strong emission of the CO2 plasma shows excited neutral O and C atoms and ionized O+ and C+ species. The medium-weak emission is due to electronic relaxation of excited species C2+, O2+, N+, N, H and molecular band systems of C2(E1Σg+–A1Πu; e3Πg–a3Πu; d3Πg–a3Πu), CN(B2Σ+–X2Σ+; A2Π–X2Σ+), O2(b1Σg+–X3Σg−), O2+(A2Πu–X2Πg), N2(C3Πu–B3Πg) and N2+(B2Σu+–X2Σg+). The characteristics of the spectral emission intensities from different species have been investigated as a function of the laser irradiance and CO2 pressure. Optical breakdown threshold intensities and plasma temperatures were obtained. The evolution of the luminous plasma was examined by time-resolved optical emission spectroscopy. The velocity distributions for different species were obtained from time-of-flight (TOF) measurements. Electron density in the laser-induced plasma was estimated from the Stark broadening method. The temporal evolution of the intensities in the TOF profiles for O+, O2+, C, C+ and C2+ species has been used for the estimation of the corresponding three-body electron–ion recombination rate constants.